Method for coating filaments

ABSTRACT

A METHOD FOR CONTINUOUSLY COATING HIGH MODULUS, HIGH STRENGTH FILAMENTS HAVING A BORON OR SILICON CARBIDE SURFACE WITH A COMPLETE AND UNIFORM DUCTILE METAL MATRIX OVERCOAT OF ALUMINUM OR MAGNESIUM COMPRISING PASSING THE FILAMENT THROUGH A PAIR OF AXIALLY ALIGNED TUBLAR CONDUITS HAVING MATABLE END PORTIONS IMMERSED IN A MOLTEN BATH OF THE METAL MATRIX MATERIAL, THE END PORTIONS BEING INITIALLY CONJOINED TO PREVENT CONTACT OF THE FILAMENT WITH THE MOLTEN METAL, AND SEPARATING THE CONDUIT END PORTIONS A DISTANCE SUFFICIENT TO EXPOSE THE MOVING FILAMENT TO THE MOLTEN METAL AND CAUSE UNIFORM COATING THEREOF.

Oct. 24, 1972 R, D..v|-:LTR| ETAL l 3,700,486

METHOD FOR COATING FILAMENTS Filed Dec. 31, 1970 United States Patent OAce U.S. Cl. 117-71 R 4 Claims ABSTRACT F THE DISCLOSURE A method forcontinuously coating high modulus, high strength filaments having aboron or silicon carbide surface with a complete and uniform ductilemetal matrix overcoat of aluminum or magnesium comprising passing thefilament through a pair of axially aligned tubular conduits havingmatable end portions immersed in a molten bath of the metal matrixmaterial, the end portions being initially conjoined to prevent contactof the filament with the molten metal, and separating the conduit endportions a distance sufficient to expose the moving filament to themolten metal and cause uniform coating thereof.

BACKGROUND OF THE INVENTION It is known to coat high modulus, highstrength filaments of, for example, boron, silicon carbide or siliconcarbide-coated boron, with a matrix coat of a ductile metal of thedesired composition by drawing the same through a molten bath thereof.One such technique is shown in copending application Ser. No. 618,514 toBasche et al. filed Feb. 24, 1967, now Pat. No. 3,556,836 and assignedto the same assignee as the present invention. Another technique isshown in U.S. Pat. 3,410,715, issued to Hough on Nov. 12, 1968. Aprocess for using such matrix overcoated filaments is disclosed in U.S.Pat. 3,443,301 issued to Basche et al. on May 13, 1969.

One of the paramount problems in coating filaments and utilizing them insuch processes resides in the difliculty of obtaining a complete anduniform coating on the lamentary substrate. In order to simplify andexpedite article fabrication, uniformly coated filaments are necessaryto consistently establish the desired filament-matrix volume ratio.Further, complete and uniform coating is necessary in order toadvantageously distribute localized mechanical stresses and thermaleffects. Although dipping a substrate in a molten bath is a known methodfor coating, the application of conventional molten bath technology tosmall diameter filaments has been disappointing in its ability toproduce complete and uniform coatings.

SUMMARY OF THE INVENTION The present invention relates to a process forcontinuously producing a complete and uniform coating of a ductilematrix metal on high modulus, high strength filaments. It contemplatesproviding an overcoat of the lightweight metals including aluminum,magnesium and alloys thereof onto such filaments as boron, siliconcarbide and silicon carbide-coated boron by passing the filamentsthrough a molten bath of the matrix material.

More particularly, the invention relates to a lfilament coatingtechnique wherein a 3-5 mil filament is initially passed through amolten metal bath via a generally horizontal immersed two-piece conduitwhich is initiaily conjoined to prevent contact of said filament withsaid molten metal and which is subsequently axially separated a distancesufficient to expose the filament and cause uniform coating thereof. Thepresent invention provides an exceptional technique wherein ingress andegress of the filament are made beneath the molten bath surface to3,700,486 Patented Oct. 24, 1972 prevent slag pickup as Well as topreheat the substrate. Further, the ability to controllably space thealigned conduits in an open or closed position not only greatlyfacilitates rethreading but also permits increased fiexibility withregard to variance of bath residence time.

BRIIEF DESCRIPTION OF THE DRAWING The invention will be betterunderstood by reference to the detailed description and accompanyingdrawing wherein the figure is a side elevation view, taken in crosssection, of apparatus capable of performing the process of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various experiments wereconducted to establish the efiiciency of the inventive technique.Silicon carbidecoated boron filaments commercially available from theHamilton Standard Division of United Aircraft Corporation, as well asfilaments of boron were at various times provided with an overcoat ofaluminum. `In general, the filaments utilized had a diameter of 3'5 milswith coatings provided thereover of 0.10 and 0.26 mil.

The boron filaments are produced by chemical deposition on a heated '1Amil tungsten Wire from a mixture of gases including boron trichlorideand hydrogen, producing filaments in general having a diameter of 3-5mils. A coating of stoichiometric silicon carbide is effected bychemical deposition on the heated boron filament from a gas mixtureincluding methyldichlorosilane, hydrogen and methane.

Referring to the drawing, a low density, ductile metal 10, of aluminumor magnesium, is melted in a steel trough 12 which is disposed in asuitable furnace enclosure shown schematically by the numeral 14. A pairof generally horizontal axially aligned, hollow tubular conduits 16 and18, preferably made of aluminum oxide, extend inwardly through the sidewalls of the trough under the surface of the molten metal bath 10. Theconduits are, of course, in appropriate sealing engagement with thewalls with at least one of the conduits being axially movable bysuitable means (not shown). As shown, the immersed inner ends areconical in a malefemale relation for mating contiguity when moved to theclosed or conjoined position. The outer ends of the conduits, which arewithout the Walls of the trough, are provided with inlets 20, 22 forcommunicating inert gas such as argon with the axially alignedpassageways 24 and 26 in order to prevent the occurence of contaminationand oxidation. As will be appreciated, a filament 28, having a surfaceof boron or silicon carbide, is adapted to pass through the passageways24 and 26 by means of the guide rolls 30 and 32 and the takeup spool 34.The passageways 24 and 26 are of a sufficiently small dimension, withregard to the surface tension forces and capillary action, to preventingress of any molten metal therein.

The filament 28 is initially threaded through the conduits 16 and 18while they are in the closed or mated position. When the desiredtemperature conditions and filament speed are reached, the conduits areaxially separated a predetermined distance to expose the filament to themolten metal and begin the coating operation. By controlling theresidence time by the rate of filament travel and the spacing of theimmersed conduit ends, as well -as the temperature of the bath, variousthicknesses and qualities of the coating can be provided. It should benoted that the sequence wherein the filament is first exposed to themolten bath and then allowed to solidify while still within an argonfilled aluminum oxide tube prevents oxidation and other contaminatesfrom affecting the overcoat, and lalso provides a gradual heating andcooling effect, respectively before and after the coating operation. Ofcourse, further preheating or cooling may be included as necessary.

EXAMPLE I In one experiment, utilizing apparatus as describedhereinabove, including two aluminum oxide tubes 16 and 18 have anoutside diameter of 1A inch and inside diameter of 1764 inch, a uniformand complete coating of 0.26 mil of commercially pure aluminum wasprovided on a four mil silicon carbide coated boron filament when thebath temperature was maintained at 750i5 C., the conduit end spacing at1/2 inchilg inch and the rate of filament travel at 1500i ft./hr.

EXAMPLE II In another experiment, using the same apparatus as in ExampleI, a uniform and complete coating of 0.10 mil of 2024 aluminum wasyprovided on the same substrate as described above when the bathtemperature was maintained at 880i10 C., the conduit spacing at 1A inchi/gg inch and the rate of `filament travel at 2400 ft./hr.

EXAM-PLE III Using the same apparatus and conditions as in Example I, auniform and complete coating of 0.26 mil of commercial pure aluminum wasprovided on a four mil boron filament.

In all cases, While measurement was difficult, the coatings effectedcovered the entire substrate boron or silicon carbide surfaces, with thecoating thickness varying at generally less than 10.05 mil.

What has been set forth above is intended primarily as exemplary toenable those skilled in the art in the practice of the invention and itshould therefore be understood that, within the scope of the appendedclaims, the invention may be practiced in ways other than asspecifically described.

What is claimed is:

1. A method for continuously coating high modulus, high strengthfilaments selected from the group consisting of approximately 3-5 mildiameter boron, silicon carbide and silicon carbide-coated boron with auniform layer of a ductile metal matrix material selected from the groupconsisting of aluminum, magnesium and alloys thereof comprising:

5 passing said filaments through a pair of generally horizontal axiallyaligned tubular conduits having matable end portions immersed in amolten bath of said metal matrix material, said end portion of each tubehaving an opening which is sufficiently large to allow free passage ofthe filament therethrough but which is sufficiently small to preventingress of molten metal therein;

said end portions of the tubes being initially conjoined to preventcontact of said filament with said molten metal, and

separating said end potrions a distance sufficient to expose said movingfilament to said molten metal and uniformly coat the yfilamenttherewith.

2. The method of claim 1 including the step of flush- 20 ing saidconduits with an inert gas.

3. The method of claim 1 wherein said filament is boron orsilicon-carbide coated boron.

4. The method of claim 3 wherein said metal is aluminum or an alloythereof.

References Cited UNITED STATES PATENTS 3,556,836 1/1971 Basche et al117-128 X 3,468,695 9/1969 Federman 117-114 C X 867,659 10/1907 Hoopeset al. 118-405 UX 2,111,853 3/1938 Fourness et al. 118-405 X 2,123,8947/ 1938 Hazelett 118-405 UX 2,231,142 2/1941 Schultz 118-405 X 3,170,9682/1965 Rokunohe et al. 118-125 X 3,410,715 11/1968 Hough 117-114 C XRALPH S. KENDALL, Primary Examiner J. R. BATTEN, JR., Assistant ExaminerU.S. Cl. X.R.

117-71 M, 114 R, 114 C, 119, 128; 118-405

